The principal objective of the proposed research is to identify and characterize some critical morphological events during the development of central nervous system synapses. Using the retiontectal system of lower vertebrates (amphibia and goldfish) as a model system, we plan to apply quantitative electron microscopical and freeze-fracture techniques to the following four major goals: 1) First, to study the assembly of membrane macromolecules at retinotectal synapses during development, with particular attention to the formation of aggregates of acetylcholine receptors and glycoproteins (using labeled snake alpha-neutrotoxins and lectins) involved in synaptic transmission and possibly in intercellular recognition; 2) Second, to compare the development and spatial ordering of retinotectal synaptic contacts (and in particular, their number and morphological characteristics) in larval and adult amphibia using a combination of degeneration and Golgi techniques; 3) Third, to characterize the distribution of junctional and extrajunctional acetylcholine receptor at retinotectal synapses during denervation and reinnervation; and 4) Fourth, to study how the system of retinotectal synaptic contacts is dynamically regulated, during functional denervation induced by alpha-neurotoxins, and during presumed hyperinnervation induced by grafting extranumery eye primordia or by deflection of a normal nerve into an already innervated tectum. Using a number of mathematic methods we have developed for quantitating synaptic parameters, we hope the proposed research to contribute significantly to knowledge of the mechanisms by which neurons recognize appropriate synaptic sites, and subsequently form, stabilize and maintain their synaptic connections.